Coil components such as surface mount-type planar coil elements are conventionally used in various electrical products such as household devices and industrial devices. In particular, small portable devices have come to be required to obtain two or more voltages from a single power source to drive individual devices due to enhanced functions. Therefore, surface mount-type planar coil elements are used also as power sources to satisfy such a requirement.
Such coil components are disclosed in, for example, following Japanese Unexamined Patent Publication No. 2006-310716, Japanese Unexamined Patent Publication No. 2012-089765, and Japanese Unexamined Patent Publication No. 2013-201375. The coil components disclosed in these documents each include a substrate, planar spiral air core coils provided on front and back surfaces of the substrate, and a through-hole conductor provided so as to pass through the substrate at magnetic cores of the air core coils to connect the air core coils to each other.